Polyvinyl alcohol fibers having improved elasticity



March 96 TETSURO OSUGI ETAL 3,

POLYVINYL ALCOHOL FIBERS HAVING IMPROVED ELASTICITY Filed Dec. 31, 1958POLYVINYL ALCOHOL SPINNING SOLUTION SPINNING ZONE STRETCHING ZONE HEATTREATMENT ZONE ACETALIZAT] ON ZONE STRETCH 1 N6 ZONE HEAT TREATMENT ZONEPRODUCT FIBERS INVENTORS TETSURO OSUGI KENICHI TANABE YOTARO KAWABE HISASHIGE YABE OSAMU MORIMOTO SADAMARU MIYAZ AKI BY 9UM6X ATTORNEY redStates This invention relates to the preparation of improved polyvinylalcohol fibers. More specifically, the invention relates to thepreparation of polyvinyl alcohol fibers which have excellent elasticrecovery and which have good stability and wet heat resistance.

It is well-known that fibers of polyvinyl alcohol can be obtained by dryor wet spinning from aqueous solutions thereof. However, such fibersshow undesirable sensitivity to water, especially hot Water. The fibersgenerally shrink more than of their length in water at roomtemperatures, and dissolve in hot water at 70- 90 C.

In order to improve the properties of polyvinyl alcohol fibers, thefibers are generally stretched during or after spinning. Additionally,the fibers are generally heat treated to further improve the propertiesthereof. The heat treatment is usually carried out at temperatures inthe range ZOO-250 C. After stretching and heat treatment, the polyvinylalcohol fibers are acetalized with formaldehyde or other aldehydes tofurther improve the properties of the fibers. Although the strength andwet heat resistance of polyvinyl alcohol fibers obtained by suchtreatment are good, the elastic recovery of the said fibers is usuallyfairly low.

It is an object of the present invention to provide a process for theproduction of polyvinyl alcohol fibers having improved elastic recoveryproperties.

It is a further object of the invention to provide a process for theproduction of polyvinyl alcohol fibers having improved elastic recoveryproperties and high wet heat resistance.

Other objects of the invention will be apparent from the instantspecification and claims.

The block diagram of the figure is illustrative of the steps which maybe employed in practicing the present invention.

In accordance with the present invention, polyvinyl alcohol fibershaving high elastic recovery are produced by subjecting polyvinylalcohol fibers to stretching after the fibers have been acetalized. Ithas been found that the elastic recovery of the acetalized fibers isgreatly improved by this stretching after acetalization. In anespecially preferred practice of the invention, the polyvinyl alcoholfibers are acetalized at least in part with a ring containingmono-aldehyde prior to stretching.

Polyvinyl alcohol which is used in the invention is a linear syntheticpolymer consisting of at least about 98% vinyl alcohol units -CH --CHOH.Polyvinyl alcohol having a degree of polymerization greater than 800 andpreferably in the range 1000-3000 is employed.

According to the invention, the polyvinyl alcohol is formed into fibers.Wet or dry spinning techniques are suitably employed. A particularlypreferred wet spinning process is described in copending applicationSerial No. 336,166 filed February 10, 1953, of Tomonari et 211., nowPatent No. 2,988,802. Other spinning techniques can be used. Duringand/or after formation of the polyvinyl alcohol spinning solution intofibers, it is desirable to stretch the fibers to a draw ratio in therange of about atent 3,027,224 Patented Mar. 27, 1962 ice 2:1 to 12:1 toimprove the strength and. other properties thereof.

The oriented fibers are preferably heat-treated prior to acetalizationat temperatures in the range of about 210-250 C. for about 2 seconds to5 minutes to improve the Wet heat resistance of the fibers.Alternatively, the heat treatment prior to acetalization can be omittedand the fibers heat treated after acetalization and subsequentstretching. Further, the fibers can be heat-treated both beforeacetalization and after acetalization and stretching. The heat treatmentcan be carried out in air or inert gases such as nitrogen, in steam, ininert molten materials such as paraffin or Woods metal, or the like.

In accordance with the invention, the oriented fibers are acetalizedwith a mono-aldehyde to a 560% degree of acetalization; that is, thefibers are reacted with a mono-aldehyde until 5-60% of the vinyl alcoholunits contained therein have been reacted. The acetalization is carriedout preferably in aqueous media in the presence of an acid catalyst.Preferably the aqueous system contains 02-10% aldehyde, 5-20% acid suchas sulfuric acid, and 0-25 sodium sulfate or ammonium sulfate. Otheracids such as hydrochloric acid, nitric acid, and phosphoric acidtogether with the salts: thereof can be used. Suitably the acetilizationis carried out at temeratures in the range 4080 C. for times rangingfrom a few minutes, e.g. 10 minutes, to a number of hours, e.g. 20hours.

In especially preferred practice of the invention, the polyvinyl alcoholfibers are acetalized to a degree of acetalization of at least 5% with aring-containing monoaldehyde. The use of ring-containing aldehydesresults in the production of fibers having improved stability andelastic recovery. Examples of ring-containing monoaldehydes which aresuitably used include furfural, benzaldehyde, hexa-hydrobenzaldehyde,tetra-hydro-benzaldehyde, ortho-, meta-, and para-chlor-benzaldehyde,2,4- dichlor-benzaldehyde, trichlor, tetrachlor and pentachlorbenzaldehyde, ortho-, meta-, and para-nitrmbenzaldehyde,salicylaldehyde, terephthalic acid aldehyde; vanillin, tolualdehyde,phenylacetaldehyde, cinnamic aldehyde, naphthaldehyde, diphenyl aldehydeand the like.

Non-cyclic mono-aldehydes can also be used to acetalize the polyvinylalcohol fibers in carrying out the present invention. Mixtures of cyclicand non-cyclic aldehydes can be used. Examples of non-cyclic aldehydeswhich can be used include formaldehyde, acetaldehyde, butyraldehyde,valeraldehyde, hexaldehyde, heptaldehyde, acetylaldehyde, nonylaldehyde,=laurylaldehyde, stearaldehyde, unsaturated derivatives thereof,methoxy-, ethoxy-, hydroxy-, chlor-, brom-, cyano-, carboxy-, sulfo-,and amino-substituted derivatives thereof, and the like. Generally,aldehydes having up to about 20 carbon atoms are suitably employed.

After the polyvinyl alcohol fibers have been acetalized, the said fibersare stretched in accordance with the invention to produce fibers havingimproved elastic recovery. The temperature at which the said stretchingcan be carried out can vary depending upon factors such as the type ofmono-aldehyde employed in the acetalizetion, the degree ofacetalization, and the like. Temperatures as low as 70-80 C. can be usedbut higher temperatures in the range -220" C. generally give bestresults.

It is usually desirable to stretch the acetalized fibers about 5 to 50%of their length although the fibers can be stretched amounts outsidethis range. It is advantageous to heat treat the acetalized fiber afterstretching since such heat treatment improves the stability and wet heatresistance of the fibers. Temperatures up to about 220 C. can be used inthis heat treatment. Longer times and higher temperatures for this heattreatment favor imaeeaaae proved stability and wet heat resistance. Itis also advantageous to permit the fibers to shrink an amount notexceeding the stretch given after acetalization during the heattreatment.

The following illustrates the advantageous efiects attained throughpractice of the invention:

Polyvinyl alcohol fibers were prepared by wet spinning. The fibers wereheat treated and acetalized with formaldehyde to 30% degree ofacetalization. Various portions of the fibers were stretched at 70 C.,100 C., 150 C., and 200 C. respectively in air for 3 minutes. Anotherportion of the fibers was stretched 20% in 3 minutes in air at 150 C.and subsequently heat-treated at 210 C. for 2 minutes during which thefibers shrank The following table shows the treating conditions as wellas the properties of the said fibers. Also presented for comparisonpurposes are the results for polyvinyl alcohol fibers spun andheat-treated similarly to those above but acetalized to 28% degree ofacetalization with benzaldehyde.

TABLE 1 had a tenacity of 3.1 g./d., elongation of 24%, and elasticrecovery at 3%, 5% and 7% elongation of 54%, 48% and 46% respectively.

Part of the acetalized fibers were stretched 10% in 2 minutes in air at170 C. Upon standing for a number of days in a room maintained at 20 C.and 65% relative humidity, the fibers shrank 1.5%. Elastic recovery ofthe resulting fibers at 3%, 5% and 7% elongation were 81%, 79% and 76%.

Another part of the acetalized fibers were stretched 28% in 2 minutes inair of 180 C. These fibers upon standing as above indicated shrank 2.6%.The fibers had a tenacity of 4.6 g./d., elasticity of 1.2% and elasticrecovery of 94% and 90% respectively at 3% and 5% elongation.

Example II Polyvinyl alcohol fibers, spun and heat treated as describedin Example I, were acetalized in a water solution containing by Weight2% n-butyraldehyde, 10% sulfuric Formalized Fibers Benzalized FibersStretching after acetalization:

Temp, Amount, percent Heat treatment after st Temp, C Shrinkage, percentMaximum Shrinkage, percent Shrinkage after standing, percent Shrinkagein Water after 30 minutes, percent:

20 C. water 0. water 80 0. water Elastic Recovery, percent:

3% elongation 7% elongation In the above table, the shrinkage uponstanding was recorded after the fibers were maintained withoutstretching for a number of days at 20 C. in a room wherein the relativehumidity was The elastic recovery was measured by stretching the fibersto the desired elongation through use of a KS Serirneter with a loadvelocity of 10 g. per minute, and after maintaining the fibers at thedesired elongation for 30 seconds, releasing the load at a velocity of10 g. per minute.

The results presented in the above table illustrate the improved elasticrecovery of fibers stretched after acetalization in accordance with theinvention. Generally greater stretching resulted in greater elasticrecovery. Both the formalized and benzalized fibers had improved elasticrecovery properties. The benzalized fibers also possessed high wet heatresistance together with very high elastic recovery properties, theelastic recovery properties thereof being higher than that of wool (88%and 83%) and nylon (86%) as measured by the same method.

As can be seen from the results illustrated above, the stability and wetheat resistance of the fibers is improved after stretching by subjectingthe fibers to heat treatment. The advantageous improvement in elasticrecovery of the stretched acetalized fibers is retained during suchsubsequent heat treatment. Fibers produced in accordance with theinstant invention find application where the properties of high elasticrecovery are necessary.

The following examples illustrate the invention:

Example I Polyvinyl alcohol fibers were prepared by wet spin ning. Thefibers were heat treated at constant length for 3 minutes in air at 230C. The heat treated fibers were acetalized in a water solutioncontaining by weight 5% formaldehyde, 15% sulfuric acid and 15% sodiumsulfate at 60 C. for 1 hour. The degree of acetalization of theresulting fibers was 32%. The acetalized fibers acid, and 20% methanolat 60 C. for 15 hours. The resulting fibers had a degree ofacetalization of 25%.

The acetalized fibers were stretched 10% in 30 secends in a liquidparafiin bath; the fibers were further heat treated in the paraffin bathat 150 C. for 20 seconds at constant length.

The resulting fibers shrank 2.8% upon standing at room temperature andnormal humidity. The fibers had an elastic recovery of 82% and 78%respectively at 3% and 7% elongation.

Example III A dry spun polyvinyl alcohol fiber was cold drawn to 130%elongation and then hot drawn to elongation in 5 seconds in hot air of230 C. The fiber was further heat-treated in hot air of 235 C. duringwhich treatment the fiber shrank 20%.

The resulting fiber was acetalized in an aqueous solution containing byweight 3% formaldehyde, 1% nonylaldehyde, 10% sulfuric acid and 60%methanol at 60 C. for 1 hour.

The acetalized fiber was drawn 16% in a Woods metal bath at C. in 10seconds. The fiber was further heat treated in the same bath at C. for10 seconds whereby the fiber shrank 3%.

The resulting fiber shrank 1.5% upon standing at room temperature andhumidity. The fiber shrank 4.6% when immersed in water for 30 minutes.The elastic recovery of the fiber at 3% elongation was 92%. Whenimmersed in 7885 C. water for 1 hour, the fiber shrank 13%. The tensilestrength and elasticity of the fiber were almost equal to those of thefiber not stretched after acetalization. Spun yarn of the acetalized andstretched fiber was blended with viscose staple fiber and was dyed in adyeing bath at 75-85 C. to obtain bulk yarn.

Example IV Polyvinyl alcohol fibers were prepared by wet spinning. Thefibers were heat treated in air of 230 C. for 2 minutes withoutstretching. The fibers were divided into portions A, B, C, and D, andwere treated as follows:

Portion A was acetalized to a degree of acetalization of 35% in anaqueous solution containing by weight formaldehyde, 15% sulfuric acid,and 15% sodium sulfate at 60 C. for 1 hour.

Portion B was acetalized to a degree of acetalization of 32% in anaqueous solution containing by weight 1.8% nonylaldehyde, 5% sulfuricacid, and 60% ethanol at 70 C. for 1 hour.

Portion C was acetalized to a degree of acetalization of 31% in anaqueous solution containing by weight 4% benzaldehyde, sulfuric acid,and 50% methanol at 60 C. for 1 hour.

Portion D was acetalized to a degree of acetalization of 26% in anaqueous solution containing by weight 5% phenylacetaldehyde, 10%sulfuric acid and 50% methanol at 70 C. for 1 hour.

Subsequently the above fibers were hot drawn to various degrees ofelongation in air. The following table shows the drawing conditions andalso presents the properties of the fibers obtained.

at 90 C. for 30 minutes, the elastic recovery thereafter being 90% and85% at 3% and 7% elongation respectively.

We claim:

1. The method of preparing polyvinyl alcohol fibers having improvedcharacteristics including high elastic recovery properties, whichcomprises spinning a polyvinyl alcohol solution into fibers, modifyingsaid fibers by subjecting the fibers to the following steps in sequence,first acetalizing 5-60% of the vinyl alcohol units of said fibers bysubjecting said fibers to reaction with a rnonoaldehyde having up tocarbon atoms in an acetalization Zone, removing the fibers from theacetalization zone, and second stretching the acetalized fibers 55 0% oftheir length in a medium selected from the group consisting of air,liquid parafiin and Woods metal at a temperature in the range or"100-220 C. whereby acetalized fibers having improved elastic recoverycharacteristics are produced.

2. The method of preparing polyvinyl alcohol fibers having improvedcharacteristics, including high elastic re cover properties whichcomprises spinning a polyvinyl alcohol solution into fibers, modifyingsaid fibers by subjecting the fibers to the following steps in sequence,first TABLE 2 Drawing Shrinkage, minutes in water Elastic Recovery,

percent Fiber Portion Elonga- Time, Temp, 3% Elon- 7% Elontion, min. C.C. C. C. C. gation gation percent talized fibers to 4.4 g./d. for thefibers drawn 20% in 2 minutes at 180 C. The elasticity of these fibersdecreased from 28% to 14%.

The fibers of portion A stretched 30% in 2 minutes at 180 C. when soakedin water for 30 minutes decreased in elastic recovery to 63% at 3%elongation and 48% at 7% elongation. On the other hand, the fibers ofportion C stretched 20% in 2 minutes at 180 C. retained the improvedelastic recovery even after treatment in water acetalizing 5-60% of thevinyl alcohol units of said fibers by subjecting said fibers to reactionwith a rnonoaldehyde having up to 20 carbon atoms in an acetalizationzone, at least 5% of the said vinyl alcohol units being acetalized byreaction with a ring-containing rnonoaldehyde having up to 20 carbonatoms, removing the fibers from the acetalization zone, and secondstretching the acetalized fibers 550% of their length in a mediumselected from the group consisting of air, liquid paraffin and Woodsmetal at a temperature in the range of l00220 C. whereby acetalizedfibers having improved elastic recovery characteristics are produced.

References Cited in the file of this patent UNITED STATES PATENTS2,636,803 Cline et al Apr. 28, 1953 2,895,786 Schlack July 21, 1959FOREIGN PATENTS 799,815 Great Britain July 24, 1957

1. THE METHOD OF PREPARING POLYVINYL ALCOHOL FIBERS HAVING IMPROVEDCHARACTERISTICS INCLUDING HIGH ELASTIC RECOVERY PROPERTIES, WHICHCOMPRISES SPINNING A POLYVINYL ALCOHOL SOLUTION INTO FIBERS, MODIFYINGSAID FIBERS BY SUBJECTING THE FIBERS TO THE FOLLOWING STEPS IN SEQUENCE,FIRST ACETALIZING 5-60% OF THE VINYL ALCOHOL UNITS OF SAID FIBERS BYSUBJECTING SAID FIBERS TO REACTION WITH A MONOALDEHYDE HAVING UP TO 20CARBON ATOMS IN AN ACETALIZATION ZONE, REMOVING THE FIBERS FROM THEACETALIZATION ZONE, AND SECOND STRETCHING THE ACETALIZED FIBERS 5-50% OFTHEIR LENGTH IN A MEDIUM SELECTED FROM THE GROUP CONSISTING OF AIR,LIQUID PARAFFIN AND WOOD''S METAL AT A TEMPERATURE IN THE RANGE OF100-200*C. WHEREBY ACETALIZED FIBERS HAVING IMPROVED ELASTIC RECOVERYCHARACTERISTICS ARE PRODUCED.